1. Field of the Invention
The present invention relates to methods and apparatus for locking a conventional personnel access door for security purposes and, more particularly, relates to improved methods and apparatus for securing a door without relying upon the hardware of a conventional door latch.
2. Description of the Background
Various types of door security devices, safety latches, door locks, and door restraint mechanisms have been devised to prevent the unauthorized intrusion of persons. Unfortunately many such devices can be picked, pried apart, or otherwise defeated by intruders, and do not offer the desired assurance of security. Other door security devices are difficult to manufacture, install or use. Many such devices include complicated and expensive parts, and accordingly are not regularly used by personnel. Finally many door security devices are functionally dependent upon the design of the door knob, and/or operate in conjunction with the striker plate in the door jamb adapted for receiving the door latch. Accordingly, such devices cannot be universally used on all doors, and the location of the security device is necessarily determined by the location of the conventional door latching device.
U.S. Pat. No. 4,281,865 discloses an inner door security device which is rather complicated in its design and use, and relies upon the door knob as a functional component of the security device. U.S. Pat. Nos. 3,666,843, 4,155,578, 4,334,705 and 4,386,797 are also directed to door locking devices, although each of these locking devices again relies upon the door knob to perform its intended function, and therefore must be located at the position of the door knob. The spacing from the door knob to the edge of the door may vary, and some door knobs are positioned near the middle of the door for aesthetic reasons. Accordingly the devices disclosed in these patents cannot be universally used for all doors. U.S. Pat. No. 3,809,418 is directed to a chain-type door locking device which functionally relies upon both the door knob and the door jamb striker plate. U.S. Pat. No. 2,396,982 discloses an alternate design for a door lock, which again relies upon a modified striker plate to perform its intended function.
U.S. Pat. No. 4,254,976 discloses a complicated and expensive door lock mechanism, which also works in conjunction with a door knob and striker plate. A significantly simpler version of a door lock is disclosed in U.S. Pat. No. 4,575,140, although this door lock again relies upon a new striker plate and a main plate which fits over the door handle. U.S. Pat. No. 3,316,005 also discloses a modified striker plate with a wing which extends inwardly from the door jamb. The device of the '005 patent includes a locking plate with a slot which slides over the striker plate wing, and a lower bar pivotable with respect to the locking plate may be positioned to prevent removal of the locking plate. U.S. Pat. No. 3,421,787 discloses a keeper plate secured to a door jamb, and a locking plate which also slides over and may be fitted with a selected groove in the keeper plate. A sliding bolt plate prevents removal of the locking plate with respect to the keeper plate. U.S. Pat. No. 4,015,869 discloses a door lock with interlocking hinge plates. In addition to being unsightly, the hinge plate concept as disclosed in this patent requires that the door itself be damaged by securing one of the plates to the door.
The disadvantages of the prior art are overcome by the present invention, and an improved door locking device and method are hereinafter disclosed which may be used to reliably prevent unauthorized intrusion. In preferred embodiments, the door locking device of the present invention need not damage or mar the door. Most importantly, the device of the present invention may be positioned at any desired elevation, and need not operate in conjunction with the door handle or conventional door jamp striker plate. Various embodiments of the present invention may employ a universal door jamb restraint, thereby reducing manufacturing and inventory costs, while increasing the versatility of the door lock to the user.